


Timing is the Key

by SlushyRain



Category: Undertale (Video Game)
Genre: Asgore doesn't like Sans because he wants to fuck his kid, But sub in the bedroom, Ecto-Penis (Undertale), F/M, Frisk Has Female Parts, Frisk can see magic, Frisk falls down with a chastity belt, Frisk is dom outside of the bedroom, Glowing semen, Hand Jobs, Hops between Frisk and Sans' thoughts and actions, I come up with the WEIRDEST shit at work, I'm sorry if its confusing, Lots of minor kinks, Multiple arcs as Frisk grows up, Non-Binary Frisk, Post-Undertale Pacifist Route, Praise, Rough Sex, Sans gets kind of rough in bed, Sans lusts after Frisk even though he knows he can't have them, Slightly possessive Sans, Soul Shenanigans, The story is in third person for the most part, This is so embarrassing to post, This is the first smut I've written in so long, Toriel is wingmom of the year, Undyne is an accidental cockblock, frisk is blind, god forgive me for i have sinned, soul bonding
Language: English
Status: Completed
Published: 2016-11-17
Updated: 2016-11-17
Packaged: 2018-08-31 13:45:16
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 14,089
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8580802
Author URL: https://archiveofourown.org/users/SlushyRain/pseuds/SlushyRain
Summary: After a particularly nasty genocide route, Frisk falls down into the Underground one final time but with a new contraption locked around their waist- A chastity belt. Sans is quick to forgive them after a heartfelt apology and a promise to free the monsters from their underground prison and vows to protect the kid. However, as Frisk grows up, things begin to get a little more complicated.





	

**Author's Note:**

> Forgive me, I have sinned so hard. I don't even know where this came from honestly. I was just waiting to clock out at work one night and this suddenly popped into my head and wouldn't leave me alone? This is hands down the longest fanfiction I have ever written, as well as the first smut I've done in a really long time. So, uh, enjoy I guess? Really nervous about posting this,,
> 
> I'm posting this in class and hoping to god no one sees my sins... Will look over and edit any mistakes later!

When Frisk fell for the fifteenth, and final time, Sans was still extremely wary and tired of them. They had just completed a genocide run in less than a week, mindlessly murdering anyone who they had the chance to find before resetting immediately. Even if they were doing a pacifist run this time, it would still take some time for him to be able to look past what the kid had done in the previous run.

Of course, he had already gone through the motions of promising Toriel that he would protect the child from the dangers of the Underground. Sans was currently lounging high up in a tree, eyes trained on the door that lead into the ruins. The dark purple stone creaked loudly, echoing through the empty forest, as Frisk shoved their entire body weight into the door. Watching this was always slightly amusing for Sans- watching a tiny eight-year-old kid that was even shorter than him trying to push open a door that was five times their height and almost six hundred pounds of pure stone? Hilarious.

Once Frisk had the door open enough for them to slip through, they stepped out into the snow and looked back from where they had just exited. Of course, they couldn’t technically see anything thanks to being blind, but with the exposure to magic and their own magic awakening, they could see the magic residue that made up every monster’s body. Frisk turned their head back around and squared their shoulders, marching down the road towards Snowdin.

Even from where Sans was sitting, high up in the thickest parts of the trees, he could hear Toriel sobbing from inside the ruins. His shoulders relaxed at the ear-piercing wail, relieved to know that Frisk seemed to be doing a clean run instead of murdering their own mother… again. Sans shifted his eyes to watch Frisk trek down the snow-covered path just in time to see them climb carefully over the giant tree branch that was in the middle of their path.

Frisk paused when they landed on the other side, glancing over their shoulder for a second to scan the path behind them, before moving forward. Sans grin widened and pulled himself to his feet, balancing on the tree branch that he had just been laying on- it was time for him to make his underground famous entrance. With a deep breath, Sans crouched then launched himself off his perch and aimed for a landing right in the middle of the tree branch laying on the path. His slippered feet made contact with the wood and it split in half with a loud and satisfying crack. Up ahead, Frisk stiffened at the loud noise before giggling and skipping the rest of the way to the bridge. Sans took his time walking behind them, using a little magic to keep his steps silent. He knew Frisk would pause at the bridge like they always did, so he had a little time to catch up.

Frisk stopped at the bridge just as he expected and he teleported the last couple of feet to land behind them. They were bouncing slightly in place, shoulders tense and their hands balled up at their sides. Sans knew that they were waiting for him to speak first, just like always.

“human. don’t you know how to greet a new pal? turn around and shake my hand.” Sans said, holding his hand out.

Frisk spun around and launched themselves at Sans with a squeal. “Sans! I missed you, I’m so sorry, you have no idea, I am so sorry! It wasn’t me, it was Chara, and I reset immediately so I could come back and apologize and I’m not going to do it again, please don’t be upset with me I’m sorry!”

By the time they had stopped talking, Frisk was sobbing and clutching his hoodie in their small fists. Frisk acted so mature and wise beyond their years, mostly due to the fact that they had been resetting for over a year and learned more every time they returned. Sans hugged the shaking child, rubbing their back in comforting circles.

“kid… are you bein’ serious here or are you just pullin’ my funny bone?” Sans asked, staring down at Frisk’s head that was buried in the thick fur of his hood. “’cause if you are, that ain’t cool. you didn’t kill your mom, so that must count for somethin’.”

Frisk stiffened at the mention at them killing their mother and pulled back to look up at Sans’ face. In their eyes, they saw a swirling mass of cyan in the shape of his skull standing out against the darkness. Sans flinched at their opened eyes, the empty brown irises staring through him.

“I’m serious. That wasn’t me… And to make it up to you and to prove that I’m really Frisk, I’m getting you all to the surface again.”

Sans opened his mouth to speak, but was cut off by Frisk’s hand slapping over his teeth.

“And we’re staying there. No more resets. I promise, I swear, I’ll even pinky promise.”

The two of them continued to stare at each other for a moment before Frisk averted their gaze. Sans’ magic was swirling inside him at an alarming pace and it was making them dizzy.

“… i’ll hold you to that, buddy.”

Frisk’s head snapped up and a grin split their face, showing off their missing teeth. Sans couldn’t help but smile back, his grin becoming more genuine and his sockets crinkling.

“Thank you, Sans!” Frisk cheered, hugging him again.

“alright, alright. lets get you home and in the bath. pretty sure you humans aren’t supposed to turn this color.”

The two of them walked back to Sans’ house, hand in hand. Frisk was swinging their joined hands back and forth and Sans went along with it, his bones clacking against each other softly. By the time they reached the Snowdin house, Frisk was shivering and huddled into Sans’ side with his hoodie wrapped around their body. Sans herded them in and Frisk sighed as warm air washed over them. The skeleton brother’s house was the same as always- the blocky TV sat on the same old table, the pet rock was still by the door covered in sprinkles, everything smelled like burnt tomatoes and spices.

Sans walked them into the bathroom that was nestled between their bedrooms and reached into the bathtub to turn the faucet on. Water rushed out of the spout and within moments, steam was slowly filling the room. Sans placed the clog in the tub and pushed Papryus’ rubber ducks into the water.

“okay, all good. lets get you out of them clothes and in there, kid.” Sans muttered, turning back to Frisk who was standing behind him still huddled in his jacket. It was way too big for them- the sleeves fell past their hands and the bottom of the jacket reached their knees.

Silently, Frisk held up their arms, watching Sans with an expectant expression. Great. They expected him to undress them. Sighing, Sans grabbed the sleeves of his hoodie and pulled it off their body. He made quick work of getting the kid out of their striped sweater, but when he was tugging their shorts off he paused and quirked an eyebrow ridge. Underwear made of mesh wire and elastic covered their lower half and a small timer sat in the middle with a jumble of numbers displayed.

“uh… kid, what is this?”

“Oh! I forgot about that. That’s, uh, my chastity belt? The orphanage put it on me after I kept flirting with the nuns,” Frisk giggled, pulling at the elastic on their waist. “They made it to where it’ll come off on its own when I turn eighteen and they used elastic around my waist so it can stretch as I grow. It’s kind of annoying but I’ve gotten used to it.”

Sans stared at Frisk, shocked by how nonchalantly they acted about the entire situation. Sans let out a bark of laughter, leaning back on his heels as his body shook. “well, good thing monster food turns into energy, huh? you’d have a messy situation on your hands if it didn’t.”

Frisk blanched at the thought, hands grabbing at the belt that encircled their waist. Sans was right- it would be impossible to properly take care of their bathroom needs with the mesh stopping them from cleaning whatever mess they made and not having the help of their caretaker who normally dealt with it.

Sans continued to laugh as he watched emotions flit over Frisk’s face. While the situation was amusing, he felt kind of bad for whoever Frisk wanted to get involved with later on in their life. The chastity belt would make any intimate situations almost impossible. Sans waved away the thoughts with a huff. The kid was just eight years old, there was plenty of time before that was a concern for them or their love interest.

 

 

Four years later, Sans was kind of regretting his decision to ignore Frisk’s chastity belt situation. When they were a kid, it was hard to distinguish their features to determine if they were male or female but when they had turned twelve it was painfully obvious what their sex was. They still insisted that everyone refer to them as nonbinary and Sans continued to value their wishes.

“Hey, Sans?”

Sans startled and his eyes refocused to look at Frisk’s stomach then travelled up their body before meeting their gaze. It was still slightly creepy to have their blank irises staring at yours as if they could actually see you when they were one hundred percent blind.

“Are you okay? You’ve been staring at me for like five minutes…” Frisk set their hands on their hips and stared down at him.

A cold sweat broke on his forehead as Frisk stared down at him. Sans tore his gaze away from theirs and stared past them at the TV that was playing some human gameshow. He honestly hadn’t mean to stare at them for so long, he had just been thinking about his current situation and zoned out.

“Sans! Don’t ignore me!”

Frisk leaned down into his line of vision, giving him a perfect look down their shirt. It took all of Sans’ willpower and conscience to shift his gaze again to look down at his lap, his fingers clacking together as he fumbled them. He knew having such feelings for Frisk was wrong, but he just couldn’t help it. He knew they were only twelve, that they were nowhere near mature enough for him to even think about pursuing them as an actual love interest, but Frisk mad it hard for him. Frisk had certainly lived up to their reputation in the underground by being a serial flirter with everyone they encountered. They constantly flirted with their own mother and wasn’t scared to put the moves on anyone that sat near them when they visited Grillby’s.

Frisk knew the effect they had on Sans. They were aware of the way that their body was beginning to mature, hips filling out and breasts growing. It was a battle not to use this new development to their advantage- they liked Sans and had for a while but knew that he would never make a move since they were so young. So, instead, they took to teasing him at every chance that had.

“Sans?” Frisk repeated, squatting down even farther so they could see Sans’ bowed face.

“u-uh… i didn’t mean to stare, kiddo. i was just thinkin’ about something and got a little numb skulled.” Sans muttered, eyes still locked on the fingers in his lap.

Frisk reached out and grabbed one of his hands and brought it to their lips, giving it a small kiss. Sans froze at the contact, his smile hardening. Their lips felt so good against his phalanges and he couldn’t help but lean into the contact. Frisk’s eyes found his again as he stared reverently at the lips that were touching his hand. It was so soft against his bones, plump and malleable. He wanted to push, pull, and pinch those lips until they were swollen and bruised to see how they felt against his fingers then. Their lips would probably feel wonderful against his ribs as they kissed downwards, trailing their fingers along his spine as they went even lower to brush against his hip bones.

Frisk stared at Sans, watching his magic churning violently in his body. It was slowly gathering in his left eye and his chest, bathing the blackness in a soft hue of cyan. Their expression softened as they watched the battle that went on with his magic- it was clear that it wanted to manifest something, anything, but Sans was keeping a tight hold on it, refusing to let it go down past his ribs. A mischievous thought passed through Frisk’s mind and they grinned.

“k-kid… what’s with that look?” Sans whispered, his voice husky from arousal.

“Nothing.”

Before Sans could respond, Frisk opened their mouth and wrapped their lips around the tips of Sans’ phalanges. A groan tore out of Sans’ throat before petering off into a high pitch whine. Frisk sucked lightly on the bones, reveling in the sounds that Sans was making. His magic was focused in his face and it was obvious that he was blushing from Frisk’s ministrations.

“kid…! y-you shouldn’t be doing shit like this!” Sans whimpered, trying to hold back his magic from forming in his pelvis. “frisk, please, i can’t take much more of this…!”

“Then just give in, Sans,” Frisk whispered, eyes lidded seductively. They pulled back from Sans to sit back on their heels, hands reaching down to grab the bottom of their sweater.

Sans watched Frisk’s hands as they moved down their body and when they started tugging their sweater upwards, another groan forced its way out of his mouth. He knew he couldn’t do this but Frisk was offering themselves to him in such an alluring way. More skin of their stomach was being revealed as they pulled their sweater up farther and Sans scooted to the edge of his seat, hands reaching for the soft skin.

Right as he was about to touch Frisk and pull them into his lap, the door rattled violently. Frisk spared a glance at the door before shrugging and continuing to pull their shirt over their head. Sans, however, had been knocked out of his daze at the sound and was frozen in place as the realization of what was happening downed on him.

“SANS? WHY IS THE DOOR LOCKED?? CAN YOU LET US IN, PLEASE?!”

Frisk sucked their teeth at being interrupted and the revealing of them locking the front door to give Sans and them a little privacy. Frisk pulled their sweater back down with a sigh and glanced back at Sans only to realize he had disappeared.

“Sans, you asshole!” Frisk shouted into the empty living room. A series of loud bangs could be heard from Sans’ room and they realized they had probably teleported there when Papyrus tried to open the front door. That sneaky bastard.

 

 

Fate was a cruel woman. Sans had figured this out the hard way as another four years passed. Frisk had matured beautifully and was no longer the scrawny child that had fallen into the underground when they were eight years old. Their hips had filled out, leaving them with a rounded waist that swayed with every step they took. They kept their breasts inside a binder, giving the illusion that they were flat-chested. Frisk insisted on having this, saying it made them felt more themselves even though they didn’t hate their chest.

“kiddo, come on now. i told you i’d get you some ice cream, didn’t i?” Sans yelled into the seemingly empty house.

It was Frisk’s sixteenth birthday today, and Sans had been put in charge or getting the teenager out of the house so Toriel and company could set up their surprise party.

“Coming, sorry! Just trying to… get this… shoe on!” Frisk replied, hopping through their doorway as they tried to wedge their foot into a sneaker.

“you should untie them. makes for easier access,” Sans mused, watching Frisk stomp their foot to get the sneaker over their heel. As Sans spoke, their eyes darted up to meet his and a sly grin spread across their face. Sans took a step back involuntarily, wary of whatever thought had just passed through Frisk’s mind.

“Easier access, huh? Wouldn’t you like that, Sansy?” Frisk practically purred, watching Sans’ magic swirl through half-lidded eyes. As if on cue, his magic began churning, gathering in his face. He was blushing again, something Frisk found was quite easy to accomplish.

With one final stomp, Frisk’s sneaker slipped over their heel and settled comfortably around their ankle. Their sneakers were bright red high tops with blue laces and soles which they wore everywhere that they went. The original pair had been a gift from Alphys when Frisk turned thirteen and they received a new pair every year with new upgrades. This year’s pair of sneakers had been equipped with barrier magic, a courtesy gift from Undyne, but the colors of the sneakers were always red and blue. Frisk suspected that Alphys designed them this way to take a teasing stab at the crush they had on Sans, but had never actually asked.

“kid?”

Frisk’s eyes refocused and they realized they were staring at the swirling reds, blues, and greens that made up their sneakers- residue magic from Undyne, Sans, and themselves. With a quick shake of their head to dispel any lingering thoughts, Frisk lifted their head to meet Sans’ gaze. His magic was drifting lazily through his body, lightly twitching at the tips of his fingers, betraying his semblance of acting cool. Sans’ magic always twitched at the ends of his phalanges when he was nervous or unsure of a situation.

“Sorry, I zoned out. You good to go, bone boy?” Frisk smiled, hopping down the steps.

Sans’ eyes followed their movement, watching their hips jiggle with every bounce. Frisk had taken to wearing a new type of pants that they called ‘skinny jeans’ and it left nothing to the imagination. It was bad for Sans because his thoughts couldn’t help themselves from drifting into forbidden territory about how he wanted to squeeze their hips, but it was also good for Sans because while he refused to act on his desires, this allowed him to sate some of his longing.

Sans nodded and turned to open the door, stepping aside to let Frisk pass through first. The bright sunlight streamed in through the open doorway and Sans couldn’t help but grin a little wider. It had been so many years since breaching the surface, thanks to Frisk’s quick work of the underground and breaking the barrier, but it still amazed him to realize that this was his life now. No more worrying about resets, about waking up to hear his brother yelling at him to wake up before he was late, wondering if this was going to be a good run or a bad run.

The two of them stepped out into the open air, pausing to let the gentle breeze wash over them. Sans let out a sigh and let his shoulder relax, while Frisk hummed a cheerful tune. They set off down the sidewalk to head towards the park where they were going to get some nice cream. A quick glance over Sans’ shoulder showed Toriel, Papyrus, and Undyne hurrying into the house that they had just left, arms full of bags and food for the party.

“So,” Frisk started, their gaze locked on the sidewalk. “What’s with the sudden urge to go get some nice cream?”

Sans glanced over at them, thankful that Frisk was a little shorter than him so he didn’t have to crane his neck to look at them properly.

“I mean, you busted in my room at nine in the morning, yelling incoherently about going to the park. I didn’t even know you were even awake that early.”

“wasn’t. paps forced me awake and told me to get you up and out of bed before pushin’ me into your room. what you heard with my half-asleep mornin’ rambling,” Sans chuckled, dropping one eye socket in a wink. “you don’t wanna get some nice cream? we can do somethin’ else if you want.”

Frisk stopped in the middle of the sidewalk and turned to look at Sans. They had another mischievous smile on their face and Sans groaned as he realized he had just gotten himself into a world of trouble.

“Can we go see a movie? There’s a horror movie that just came out and I heard it’s really scary!” Frisk gushed, leaning forward to wrap themselves around Sans’ arm. He froze at the blatant show of affection, extremely aware of the way that he could feel the softness of Frisk’s chest through the multiple layers of clothing.

“u-uh, sure, kid. wanna shortcut there or walk it out?”

“Shortcut, please!” Frisk quipped, holding onto Sans’ arm even tighter in preparation of travelling through the void.

“alright, alright. you know the drill: hold on tight, don’t let go, keep your hands and feet inside the ride at all times…”

Before Frisk could respond, they felt the tugging sensation in their soul. Magic was swirling around Sans’ body in a chaotic manner, squeezing together to shrink. They watched the magic shift, growing smaller and smaller before exploding back into its original form. Teleporting with Sans was one of their favorite things to go, without a single doubt. Sure, it was nice being so close to the object of their affection, pressing against his arm and having the musky scent of his hoodie envelope them. But, what really made it exciting was being able to watch the shifts in Sans’ magic. His magic would churn as it shrunk, preparing to slip through the very fabric of time, before exploding back into place as if it was made of elastic when they reached their destination.

“we’re here.”

Sans was relieved and upset when Frisk released his arm, stepping back to take in their surroundings. He loved teleporting with Frisk, how they would press themselves up against his body until he couldn’t tell when he stopped and they began. They were the only one who would willingly travel with him through the void, which made the trip even more special knowing that they actually enjoyed it and didn’t do it for the convenience of getting somewhere faster. Sans’ eyes tracked Frisk’s movements as they reached up to smooth down their chestnut brown hair, letting it settle around their shoulders in silky waves.

“Come on! Let’s go, we need to make sure to get popcorn and drinks before the movie starts and to find good seats!” Frisk squealed, grabbing Sans’ hand to drag him through the front doors of the theater.

It was practically empty inside the theater, the only people present were the employees that were lounging at their stations as they scrolled through their phones. Frisk dragged Sans up to the window, tapping on it lightly to get the attention of the cat monster that was dozing slightly. He jumped at the sudden sound, fur puffing up around his neck as he looked around wildly looking for the source of the noise.

“Hi, BP!” Frisk smiled, waving. “Can we get two tickets to _The Conjuring_?”

“Hey, buddy. Comin’ right up.” Burgerpants grinned, printing their tickets and sliding through the bottom of the window. “There ya go. Gonna be a solid twelve dollars.”

Sans fished his wallet out of his pockets, pulling the right amount of money from it and slid it under the window to Burgerpants.

“thanks, bp. ‘preciate it, good luck with your exams next week.” Sans winked and let himself be pulled away by Frisk’s insistent tugging.

After buying a bucket of popcorn that was bigger than Frisk’s head and a gigantic drink that Sans had to hold with both hands, the two of them found their way into viewing room six. It was the farthest room on the left wing of the theater and as they walked in, Sans realized it was completely empty and the opening previews were already playing.

“Hurry! It’s gonna start soon. Let’s sit in the back, we’ll have a perfect view of the screen from up there!” Frisk giggled, skipping up the stairs.

Sans followed at a slower pace, watching Frisk’s ass bounce with every step they took. A smirk tugged at his mouth as he enjoyed the view. Sans always preferred to walk behind everyone for this specific reason- to watch Frisk’s hips sway and bounce as they walked. His eyes were trained on the rhythmic sway of their hips, so zoned out that he didn’t realize when Frisk stopped walking and almost ran skull first into their ass. He stumbled to a halt just in time and he could hear Frisk laugh from the step above him.

“You alright, Sansy? The shows on the screen not right here,” Frisk whispered, turning to look down at him. “Though I wouldn’t mind changing our plans…”

Sans face immediately busted in a bright glow, cheeks flaming with embarrassment and arousal at Frisk’s words. Without saying anything, he pushed past them to take the last couple of steps to the top row and sat himself down in the middle. Frisk followed him, laughing quietly at his flustered appearance.

After a beat of silence, Sans couldn’t stop the question from bubbling out of his mouth.

“why do you tease me like this, kid?”

“What?” Frisk questioned, turning their body to face him.

Sans shoved his hands into the pockets of his hoodie and hunched his shoulders to bury the bottom of his face in the fur lining his hood. “you always flirt with me, saying things to… get me going. why?”

“Because I like you. Why else?”

It was like time had stopped for the two of them as Frisk’s words registered in Sans’ mind. They liked him, apparently. Could he trust what they said? Frisk hadn’t lied about much in this timeline and had even kept their promise to get them to the surface and not reset again.

“Yes, I mean it. I’m not lying, Sans.” Frisk sighed.

Sans jumped at their voice, surprised that they had known exactly what he was thinking. He chuckled nervously. “but, why? i’m just a bag of old bones, kid. you could do so much better.”

Frisk pouted at Sans’ self-deprecating words and reached over to grab one of his hands out of his pockets. They ran their fingers over his softly, memorizing every ridge and bump that decorated his bones. They were cracked and scratched from his work with Alphys in the lab, taking care of Papyrus, and the many timelines that Frisk had put him through. Frisk loved every single scratch on his bones and lifted his hand to their mouth to kiss at each one that they found.

“I like you,” Frisk kissed the scratch on his index finger that he had gotten from a stray piece of metal snagging him when he was working on one of the reactors in the core. “because you’re so funny,” Another kiss was placed on his palm, where Frisk had sliced his palm open during one of their rougher resets. “because you care for me more than you think I realize,” Soft lips grazed his roughed-up knuckles, scratched up from the training he used to do with Papyrus as a kid. “because you’ve always been there for me when I needed you,” One more kiss was placed on the tip of his pinkie finger, where a small crack ran from the tip of his bone to his first knuckle that was due to Frisk slamming the door on his fingers during one of their games of tag.

Sans’ breathing was growing heavy as Frisk continued to place kisses on his hands and he felt so exposed. His face felt as if it had been submerged in a bucket of ice, a bright blue covering his face. Frisk continued to place small kisses along his fingers, murmuring the memory associated with it, as Sans stared at them with awe, adoration, and pure love.

Sure, Sans knew he had a thing for Frisk, but he always thought it to be more of a sick fascination since they were human. Now, though… Now Sans couldn’t lie to himself anymore. He was irrevocably in love with Frisk, the same child that had destroyed his life and then pieced it back together with soft touches and whispered promises. Eight years of helping to take care of them, sleepless nights spent laying in the living room surrounded by pillows and huddled together under blankets as they watched Disney movies. Hours of laying together in Sans’ bed as Frisk sobbed into his shoulder, stumbling over a stream of apologies. Countless times of knocking on the bathroom door for Frisk to check on Sans and to hold him as he shook violently from the flashbacks that plagued his dreams.

“… frisk.”

With one final kiss to Sans’s wrist, Frisk pulled back to look at Sans. Their face was flushed, hair sticking to their forehead, and they were squirming in their seat.

“are you really serious? i know i asked already, but… this isn’t a game to me, buddy.” Sans whispered, reaching forward to brush his fingers against Frisk’s cheek. They leaned into his touch, eyes focused on his own.

“I’m serious, Sans. I’ve liked you since I was like, ten,” Their hand reached up to cover Sans’, intertwining their fingers together. “Do you remember when you and Paps took me out to the skating rink as a celebration of skipping the sixth grade? You held my hand the entire night, teaching me how to skate even though I kept bumping into you. Then, when you let me go and I started skating on my own… I turned to look at you and give you a thumbs up to let you know I was okay. Your… your magic was so beautiful that night, Sans. It was swirling through your body, all the way to your fingertips then back to your chest to create a sparkling vortex that lit up the darkness. That was the moment I knew I would do anything to continue seeing that reaction from you and that I wanted to make you feel like that again.”

Sans’ jaw was literally hanging open with the confession of Frisk’s love. It was a shock to him that Frisk actually liked him and that they had liked him longer than he realized his own feelings. With a small giggle, Frisk closed Sans’ mouth, letting their hand linger on his cheek. Just as Frisk was doing, Sans leaned into their touch.

“this seems so unreal…” Sans whimpered, letting his hands dip lower to rest on Frisk’s waist. “i never even dreamed that i would have a chance with you.”

Frisk scooted closer to Sans, lifting their legs to drape them across his lap. They pushed the armrest between them up with a huff of annoyance, allowing the two of them to be even closer. The movie played on in the background, its audience of two paying no mind to what was taking place on the screen.

“Are you kidding me? I never thought that I would have a chance with you!” Frisk chuckled, pressing closer against Sans’ side. “You’re way out of my league, Sans. I thought I had been like family zoned since the beginning of time.”

A rumble of laughed shook Sans’ body. “you were at first, i won’t lie. i refused to even let myself think of you as more than just frisk… i felt so dirty for findin’ you attractive.” Sans magic dulled, the cyan color fading until it was just a soft light. “when you were twelve is when i finally accepted that this was my life: lustin’ after the child that i had murdered, raised, and saved, dozens of times. i mean, i knew i liked you since you were a kid, but i didn’t realize it was this way…”

Frisk had the largest smile on their face, ecstatic at Sans’ confession. Without missing a beat, Frisk shifted their position and threw one leg over Sans’ lap, allowing them to straddle the skeleton.

“f-frisk?! what are you doin’, kiddo?!” Sans sputtered, magic spiking and swirling.  “we’re in a mov-“

Sans was cut off by Frisk’s lips pressing into his own. His shoulders sagged at the contact, eye sockets fluttering closed as he let himself blissfully enjoy the soft skin pushing against his bones. A small whine built in the back of Sans’ throat and he gripped Frisk’s hips, pulling them closer. Frisk let out a startled gasp at the sudden movement before letting it change into a breathy moan.

Opening his mouth, Sans formed his tongue and hesitantly pressed it against Frisk’s lips. Without hesitation, they opened their mouth to meet the glowing blue with their own fleshy pink. The sound of soft moans, panting breaths, and grunts, filled the empty theater with the movie completely forgotten. 

“Stars, Sans… This is so g-good,” Frisk whispered, leaning back to catch their breath. Their face was flushed and a small trail of drool was running down their chin.

With eyes half-lidded, they observed Sans’ magic as it twisted inside his body. It was easy to see the complete outline of his body with how bright his magic was and how must it was swirling through his bones. Frisk could easily count every rib in his chest, see the holes in his sacrum, and where his fingers ended and their own body began. Sans’ magic was sparking with pure energy, small embers floating off into the darkness before fizzing away. It was like nothing Frisk had ever seen before; they had thought the night at the skating rink was special, but this was on a whole new level. Just knowing that they had caused this reaction by kissing him filled them with heat.

Unable to stay away, Frisk pressed themselves closer to Sans. They felt so far away from him, their clothes creating a barrier that was getting more annoying with each passing second. With a sharp huff, they reached down and tugged their sweater over their head, leaving them in only a bra. Sans’ magic dulled for a second before bursting back to life with an even brighter burn than before.

“oh, f-fuck…” Sans groaned, eyes roaming over Frisk’s chest. He was eye-level with their bra, the bright blue color invading his vision. “heh… did you pick this one out while thinking of me, kid?”

“I did, actually.”

Sans snapped his mouth shut, the embarrassment of the statement too much for him to form a response. Instead of speaking, he let his hands wander to tell Frisk just how much that meant to him. The tips of his phalanges rubbed soothing circles into their hips, teasing the waistline of the black jeans they had on. Frisk sighed at the contact, relishing in the way his cold bones felt against their warm, bare skin.

He loved seeing how only his touch could relax Frisk in such a way. Their shoulders were slumped, head bent forward and almost resting against his own. Their hips were pressed flush together and Sans could feel the heat emanating from their core, sending metaphorical goosebumps over his bones. With a single movement, Sans thrust his fingers inside the waist band of Frisk’s jeans, chuckling at the startled hiss from the other party.

“Sans! Your hands are cold, give me some kind of warning next time!” Frisk pouted, leaning back to give him their puppy dog face.

“sorry, kiddo. couldn’t help myself, needed to break the ice somehow.” Sans’ fingers continued to inch farther inside Frisk’s pants, slowly gliding around to cup their ass. He recoiled slightly when his fingers bumped into a hard fabric and realization hit him like a ton of bricks.

“fuck, frisk! your damn chastity belt- we can’t do shit,” Sans whined, fingers poking at the offending article of clothing.

“Awh, shit, I actually forgot…” With a small sigh Frisk unbuttoned their jeans to reveal the blinking red digits.

730 days. Another 730 fucking days until the stupid thing came off and they could do whatever they wanted.

“well, i mean, if we’re bein’ honest here,” Sans snickered, poking at the lights. “those people from your orphanage were right. you were a huge flirt and if this hadn’t been then biggest cockblock of the century, you may have had 207 bones instead of 206.”

Frisk gasped at Sans’ jokes. “I’ll have you know that I haven’t even done anything more than flirting with others!”

“wait, you mean you haven’t held hands or kissed anyone? not even monster kid?”

“No! MK is just a friend, I told you that! But, no, I really haven’t…” Frisk averted their gaze, a blush slowly creeping up their cheeks. “You were my first kiss and stuff…”

Sans’ soul hummed with pure love and happiness at that fact. “awh, kid, you shouldn’t have!”

“Shut up, Sans!”

Laughter filled the movie theatre as the two of them laughed off the conversation. Frisk turned their head to look over their shoulder, where the movie was nearing the end, and Sans followed their gaze.

“… Can I ask one question, Sans? No, two, actually.”

“of course.”

“So, what does this make us?”

Sans thought about it for a moment, bones continuing to slowly stroke the skin at Frisk’s hips. What did this make them? Sans liked- no, loved- Frisk, and Frisk returned his feelings. Were they dating, now? Or was it that awkward in-between stage where both parties were too scared to commit?

“uh… i honestly don’t know, kiddo.” Sans muttered, staring at his bones against Frisk’s flesh. He loved to see the contrast of the porcelain white to the rich brown.

“Well… Would you be my boyfriend, Sans?” Frisk whispered, their face burning with an intense blush.

Sans’ smile widened so much he thought it was going to shatter his cheekbones. “i think i might have to say yes to that question.”

Frisk squealed with delight and leaned forward to press another kiss against Sans’ teeth, humming with happiness. Their hands reached up to cup Sans’ cheeks and with a tilt of their head, they deepened the kiss. With a tentative touch of Frisk’s tongue to his teeth, it delved even farther as they began their battle for dominance.

After a few minutes of the heated exchange in which Sans had clearly won if his proud smirk and hooded eyes were to go by, Frisk pulled back to catch their breath.

“Wow. Just… Wow.” They sighed, shivering slightly at the after effects of the kiss. “So about that second question.”

“go for it.”

“Why did you go along with my idea to go to see a movie? I’m blind.”

 

 

The next two years passed by at an agonizingly slow pace. Sans had a mental countdown going in his head, waiting with bated breath until he could take Frisk as his own for the first time. The two of them passed the time with heated exchanges anywhere they could get away with; Sans’ bedroom, Frisk’s bedroom, Grillby’s… you name it and they’ve probably got some kind of story to tell from their time spent there.

Of course, their friends had quickly noticed the change in their relationship. Alphys had almost fainted from pure excitement, babbling about how her ship had finally sailed, and Undyne couldn’t hold in her own girlish squeals.

Papyrus had been ecstatic for Sans, which was no surprise. He was so happy that his brother had found his special someone, and without missing a beat, had revealed to Sans that he and Mettaton were together. Sans wasn’t sure how he felt about that particular development, but he knew Paps was his own skeleton and could be in a relationship with whomever he wished… That didn’t stop him from sharing some words with Mettaton, though.

Toriel and Asgore had probably taken the news the worst. While Toriel had somewhat come to terms with their relationship, she still had qualms about them displaying public affection around her. Sans had caught her with an unreadable expression one night when they were over at her house for dinner when Frisk had leaned over to plant a chaste kiss against his cheek. He made sure to talk to Frisk about being so affectionate to each other in front of Toriel and they agreed to keep it to a minimum. Asgore didn’t even speak to Sans for months after finding out that he and Frisk were dating- it was easy to tell that he was very upset about the entire ordeal. One of his most trusted subjects dating his own child? It was scandalous to say the least.

“SANS!”

Startling slightly, Sans snapped out of his thoughts as his brother’s voice dragged him back into the present. His eyes wandered until they settled on the tall figure standing in the doorway of the kitchen.

“yeah, bro?” He mumbled, raising his arms above his head and stretching.

“DO NOT “YEAH, BRO?” ME! YOU HAVE BEEN IGNORING ME FOR THE LAST FIVE MINUTES!” Papyrus stopped his foot with a huff. “I WAS TRYING TO TELL YOU THAT YOU MUST GET READY SOON! TORIEL WOULD LIKE US TO ARRIVE EARLY FOR FRISK’S PARTY TO HELP SET UP.”

Oh yeah, tomorrow was Frisk’s eighteenth birthday. Sans thought that he would have been paying attention, but his mindless thoughts had probably distracted him.

“got it, bro.” Sans replied, standing up and dusting off his blue hoodie. “’m ready.”

“HOW QUICK! I WILL BE READY MOMENTARILY- I MUST FINISH THE BIRTHDAY SPAGHETTI!”

Within minutes the two brothers were walking down the sidewalk towards Toriel’s house, chatting about what they had gotten the birthday child. Frisk was out with Alphys and Undyne this year at the gym that Undyne owned. They had decided to spend the day swimming and Alphys had spent days preparing the pool with her magic so Frisk could swim without worry of bumping into the concrete walls.

“KNOCK, KNOCK!” Papyrus announced, knocking on the purple door to Toriel and Asgore’s home.

A muffled reply could be heard from the other side and after a brief pause, the door opened to reveal Toriel. She had traded her traditional purple robe for a soft green sweater and a flowing white skirt that fell to her ankles.

“Hello!” Toriel smiled, stepping back to let the two skeletons in. “I’m surprised that the two of you are actually here on time. I figured a certain someone would be too lazy to get off his couch.”

“you know me too well, tori. paps basically had to drag me all the way here.”

“DO NOT LIE! YOU WALKED HERE BY YOURSELF!”

The three of them made their way to Toriel’s kitchen with lighthearted bantering filling the silence. As they rounded the corner, Asgore turned towards them from his seat at the table and made eye contact with Sans.

“Sans.” Asgore acknowledged, staring at him with a guarded expression.

“asgore.” Sans replied in the same tone of voice even though his relaxed posture betrayed him. He wasn’t in the mood to be passive aggressive with the king- today was Frisk’s day and he wasn’t going to let some petty dispute ruin it.

“Asgore. Stop it.” Toriel sighed, stepping in front of the seated king, hands on her hips. “I am tired of you behaving like a petulant child over Frisk and Sans’ relationship. They are both consenting adults and very happy.”

“I… I know, Tori. I just… Frisk…” Asgore sighed, resting his face in his palms. “I am not ready for them to grow up!”

Asgore’s quiet sobs echoed through the kitchen and Sans’ felt guilt crawl along his bones. He took a few steps until he was beside Asgore and raised a hand to pat the goat monster’s shoulder.

“look, asgore. i’m sorry about all of this, i really am.” Sans started, shifting from foot to foot. “frisk makes me really happy and from what i can tell, i make them happy. i know you probably don’t really approve of me since i worked under you as the judge, but… i’m not givin’ frisk up.”

Without waiting for Asgore’s response, Sans turned around and walked out of the kitchen. He could hear Toriel following him, the sound of her feet padding quietly behind him. They ended up in the living room, the TV playing quietly to the empty room.

“Sans…”

“what’s up, tori?”

“I’m proud of you.” Sans could hear the smile in Toriel’s words. “I know that you love Frisk and it is quite obvious to those around you. That is why I wanted the party to be the day before their actual birthday so the two of you could be together tonight and tomorrow, without interruption.”

Sans turned around to gape at Toriel’s confession, a blue hue creeping into his cheekbones. “y-you what?”

“Do not play coy with me, you bonehead!” Toriel chided, laughing quietly. “I am very aware of the… escapades you two participate in. Frisk does not always wear their sweater, you know.”

In seconds, Sans’ entire skull was burning with a blue blush. Toriel had seen the marks that he had left on Frisk’s skin and had known about how physical they were for who knows how long. Not to mention, some of the marks he had left were… interesting to say the least.

“oh my god i am so sorry,” Sans whispered, ducking his head into his hoodie. “i didn’t ever think you’d see those, oh my god, i’m goin’ to kill frisk...”

“Do not worry, Sans, I am not upset. Just be safe, that is all I ask.”

Sans groaned as he realized he was getting ‘the talk’ from the mother of the person he was involved with.

“Now… I will convince Papyrus to have a sleepover here tonight so that you and Frisk may have some alone time. I have already spoken to Frisk about this as well, so once the party is over the two of you are free to leave without hesitation.” Toriel pulled Sans into a hug, ignoring the grunts of protest from the skeleton.

“i… thanks, tori. i appreciate it.”

“No problem at all, my friend! Now, let us go back to the kitchen- Frisk shall be home soon.”

As if on cue, the front door slammed open, making Sans freeze.

“WHAT’S UP, PUNKS! We’re back!” Undyne’s voice reverberated through the house.

“Mom? Dad? Where are you?” Frisk’s voice followed Undyne’s. Their footsteps were getting closer to the living room and Toriel stepped in front of Sans.

“Go! Hide, they cannot know you are here yet!” Toriel whispered to Sans over her shoulder, winking at his shocked face. “Go to their room, I will send them up in just a moment. Just make sure to bring them back in time for their party!”

Sans nodded and shot Toriel a wide grin. “thanks, i appreciate it.” With a wink, Sans disappeared into thin air and reappeared in Frisk’s room. It was messy, the kid’s clothes thrown haphazardly across the room. His eyes found a pair of Frisk’s more risqué underwear handing from the side of their bed and with a smirk, he snatched them up to inspect them closer. The baby blue fabric was soft against his fingers and the black lave that framed the trim made him soul stutter.

“Sans! What are you doing?!”

Sans jumped and stuffed the panties into the pocket of his hoodie before turning to look at the door. Frisk was leaning against the frame, watching him with a smirk on their face as his magic slowly thrummed back to life after being caught.

“i, uh…” Sans stuttered, averting his gaze and rubbing the back of his neck.

He could hear Frisk’s chuckles as they stepped into their room, closing the door behind them softly. With a few steps, they covered the distance until they were standing in front of Sans and looked up at him with a coy smile.

“Did you enjoy snooping in my room, Sansy?” Frisk whispered, letting one of their hands play with one of the strings from his hoodie. “Were you hoping that I would catch you doing something naughty?”

His breath caught in his throat and he squeezed his sockets shut at how seductive Frisk was sounding. Sans could already feel his magic swirling, trying to gather in his pelvis. After a moment, he reopened his eyes to look at Frisk.

They were standing close to him, looking up at him with half-lidded eyes and a small smile. Their hair was tangled and wet from their swimming, dripping onto their bare shoulders. His eyes traveled farther down, taking in their swim suit that clung to their body in all the right places. The purple bikini was tied tight around their neck and left very little to the imagination as it bared the swell of Frisk’s breasts to anyone who looked. It was thin enough to see their nipples pressing against the fabric and Sans’ breath hitched at the sight.

“holy shit.”

Frisk took another step closer, pressing their chest against Sans’, and let out a small groan at the friction. “You like what you see?” They smirked, all pretense of playing coy gone.

“fuck yeah i do,” Sans panted, grabbing Frisk’s hips roughly. “you have no idea, frisk.”

“Mmm, I think I might have an idea…”

Standing on the tip of their toes, Frisk pressed their lips against Sans’ teeth and it was like a switch was flipped. Sans’ hands reached down to cup their ass to lift them up and they wrapped their legs around his hips in one fluid movement. A small gasp tore out of Frisk’s mouth as Sans slammed them into the wall, but it was swallowed by Sans’ mouth as he kissed them again. His hips grinded in an upwards motion as he opened his mouth to lick at Frisk’s lips, begging for entrance.

“O-oh, stars… Sans,” They moaned, wrapping their arms around Sans’ neck and running their hands across the back of his skull.

“fuck, babe, keep saying my name,” Sans panted, grinding even harder against Frisk’s core. He could feel how hot they were through their clothes and it took all of his willpower not to rip the fabric off of their body.

“Sans, please, I-“ Frisk stuttered, grinding back. Their breath was coming out in short pants as they pulled him closer, forcing his cock to brush against them again. “Yes!”

“And then Frisk just fucking jumps into the pool with all of their clothes on! I was so proud of them!”

At the sound of Undyne’s voice, the two of them froze. They could hear Undyne stomping down the hallway towards Frisk’s room and the heavy padding that followed them meant Toriel was following.

“you gotta be kiddin’ me,” Sans groaned, resting his forehead against Frisk’s. “damn it all. sorry, kid.”

As soon as the apology left Sans’ mouth, the door to Frisk’s bedroom slammed open.

“HEY PUNK, ARE Y- Oh.”

Sans looked over his shoulder to see Undyne staring at the two of them with a shocked expression. Toriel stood behind her, eyes wide, but her shoulders were shaking with silent laughter.

“’sup.” Sans monotoned.

“Hiya.” Frisk waved with a smile, even though they were still pinned against the wall by Sans’ body.

“ohmygodI’msosorryIdidn’tknowyouguysweredoingthisI’mjustgoingtogoBYE!” Undyne rushed, slamming the door shut before running down the hallway.

Silence filled the room for a moment before a quiet knocking sounded at the door.

“My child, we will be downstairs,” Toriel said through the door. “I would like if the two of you could come down once you are decent.”

Without waiting for a reply, Toriel padded back down towards the kitchen presumably to let everyone else know that Frisk and Sans would be joining them soon.

“Well, that was interesting,” Frisk chuckled, pushing Sans away slightly so they could slide out of their grasp. “Guess I need to change, now.”

Sans whined, grabbing at Frisk and burying his head against their neck. “nooooooooo.”

“You can watch me change.”

Sans immediately took a step back and dropped to the ground, sitting cross legged, while he looked up at Frisk expectantly.

“go on.”

Laughing, Frisk walked over to their dresser to open some drawers as they searched for clothes. With a triumphant shout, they pulled out a blue tank top and baggy black shorts and shot Sans a mischievous glance.

“These look like a certain skeleton I know would wear them.” Frisk mused, waving the clothing slightly.

“when did you steal some of my clothes?”

“Last time I stayed over.”

“but i didn’t even let you borrow any,” Sans rested his chin in his palm. “did you steal them from my closet?”

“Yep.” With a wink, Frisk reached upwards and pulled at the strings that held up the top of their swimsuit. It fluttered down around their chest, leaving their breasts exposed to the cool air. They could see Sans’ magic pooling again in his pelvis and their heart throbbed with love. Reaching behind them, they tugged on the string that was keeping the bikini attached to their body and let it fall to the ground with a wet thump.

Sans’ eyes were trained on every move Frisk made, and when their top completely fell to the floor he couldn’t stop himself from pulling his cock out of his shorts and began to pump himself slowly.

“keep going.” Sans demanded, his gaze raking over Frisk’s body. His tongue peeked out of his mouth to lick across his teeth as he continued stroking himself.

Turning around, Frisk stuck their thumbs into the band of their bottoms and slowly began to push them down. Their hips swayed from side to side as they worked the wet fabric, exaggerating their movements when they heard Sans gasp. Bending forward, they shoved the bikini bottoms the rest of the way down, leaving their ass bared and covered only by their chastity belt.

“holy fucking shit, you’re so beautiful,” Sans moaned, his pace picking up. He could feel himself getting close already; the effect of seeing Frisk’s bare body for the first time and in such an intoxicating way was too much for him.

“Baby…” Frisk whispered, sitting down on their knees in front of Sans. They pushed their breasts together as their eyes were glued to the magic swirling in Sans’ dick. “Cum for me.”

Sans moaned at the commanding tone that Frisk took, and with a final stroke and gasp, he came. It covered the front of his hoodie in small dots of glowing blue magic and Frisk reached out to swipe their fingers across his hoodie, grabbing some of his cum, and stuck their fingers in their mouth.

“… Why do you taste like blue raspberry?”

 

 

Frisk’s birthday dinner passes slowly, two hours of agonizing laughter, food, and presents. Sans kept shooting Frisk heated glances, licking his teeth when they made eye contact. Frisk kept their hand on his leg throughout the night, running their fingers up and down his femur.

Papyrus got Frisk a Rubik’s cube, saying that they could use it to improve on their puzzle solving skills and that once they master it, they would be on par with The Great Papyrus. Undyne and Alphys got them a pair of boxing gloves and a box set of an anime called _Mahoutsukai no Yome_ , which earned the pair a playful glare and chuckle. Asgore and Toriel gave Frisk the largest present of the night: a brand-new gaming computer.

Frisk squealed with delight at the gift and immediately turned to Sans with a smile. “We can play games together again! Just like we used to!”

“oh, yeah,” Sans chuckled. “we can play some games, alright.”

Everyone at the table, excluding Papyrus, caught Sans’ double meaning, causing a chorus of his name to go around the table. He held his hands up in surrender, bones shaking with laughter.

“Alright, everyone,” Toriel said, pushing her chair back and standing up. “Let us move to the living room and watch a movie!”

Papyrus shot out of his chair and began sprinting towards the living room. “I AM PICKING OUT THE MOVIE!”

“HEY, WAIT! No, you’re not, I want to pick!” Undyne shouted, following after him.

“I, uh, b-better go after them… g-goodnight, Sans, F-frisk!” Alphys smiled, trotting after her girlfriend.

Asgore nodded at Sans before leaving the room without saying anything. Toriel shook her head at his retreating figure before turning her gaze to Frisk.

“Have no worries, I will keep Papyrus here tonight. I hope the two of you have fun,” Toriel smiled softly at the two of them. “Do not do anything… too extensive.” Toriel focused her gaze on Sans, eyes full of unspoken threats.

“whoa, whoa, i’ll be the perfect gentlemonster.”

“Gentle my ass,” Frisk muttered under their breath, causing Sans to let out a bark of laughter at the unexpected comment.

“you gotta ask nicely, kiddo,” Sans replied, sliding an arm around their waist.

“Alright, get out of here you two. Bring them back home tomorrow whenever you, ah, find the time.”

“sure thing, tori. you know how punctual i am.”

“Do not make me regret this, Sans,” Toriel warned, shaking her head as she walked out of the kitchen.

Frisk scooted closer to Sans once their mother exited the room, throwing their legs over his lap. Pulling them against his body, Sans rested his chin on top of their head and let out a pleased hum.

“Less than an hour, Sans.”

“guess we better get going, huh?”

“Please.”

The familiar tugging sensation pulled at Frisk’s soul and they watched Sans’ soul do its thing: shrinking slowly, before bursting back into its previous shape as they landed in Sans’ room. The bed creaked under them at the sudden weight and Frisk dropped backwards to lay on his bed, letting out a soft sigh. Sans crawled over their body, hovering above them with his famous shit-eating grin in place.

“come here often?” He whispered, eyes half lidded.

“Not yet, I haven’t,” Frisk winked, wrapping their arms around Sans’ neck.

Sans let out a laugh at the joke and nestled his neck in between Frisk’s shoulder and neck, inhaling their scent. They always smelt like fresh snow and strawberries for some reason, probably due the kind of shampoo they used, but Sans had never found a smell he liked more.

“so.” Sans whispered, his face still pressed against Frisk’s skin.

“So.”

“we’re doin’ this.”

“Yep,” Frisk mused, petting the back of Sans’ skull with tender strokes of their fingertips. “You do want to? Right?”

“yeah! hell yeah, you have no idea,” Sans blushed at how bold his words were. “i know it was bad of me to be pinin’ after a kid but now that i have you, i ain’t lettin’ go.”

“Good. Don’t want you to.”

Frisk turned their head and pressed a gentle kiss to Sans’ forehead, humming with happiness and love. They could feel their own soul beating rapidly, beginning to synch tempos with Sans’ as they laid together in bed. Frisk knew what this meant; Toriel was the perfect educator, even when the situation became awkward.

“Sans?” Frisk asked, eyes glued to the swirling mass of blue magic in his chest that surrounded his own soul.

“mmm?”

“Would… Would you bond with me?”

Sans lurched back and out of Frisk’s grasp, their hands reaching after him before dropping on the mattress with a small thump. They turned their face away from his piercing gaze and Sans could see the flush creeping up their neck and into their cheeks.

“kiddo. do you have any kind of idea what the hell you just asked?”

Frisk nodded, head still turned to the side with their eyes squeezed shut. They looked so nervous and pitiful, Sans couldn’t be mad at them. Of course, he wanted to bond with them- Monsters just knew who they were supposed to be with. It was something engraved in their soul and with every moment spent around Frisk it beat with the need to make them his. Humans, though… Humans were a completely different story. Sure, Frisk was unique case with their ability to see magic to make up for their lost eyesight, but humans didn’t know when they were with their soulmate. It was impossible for them to truly know aside from the subtle signs that a soul might send that they always called a “hunch”.

“I… Toriel and I have talked about this before. She never kept me in the dark about how monsters married or uh… reproduced,” Frisk mumbled. “Just look at our souls, Sans. Tell me that I’m wrong.”

Sans did as they said and let his right eye flare with magic as he inspected the two souls in the room. His own soul was thrumming with blue tinted energy, beating at a lazy pace that matched Sans’ personality perfectly. Frisk’s soul was the same candy red that had been around since they were a kid and instead of it beating erratically like it always had, it had slowed down exponentially. The bright red soul was only a beat or two behind the upside down white one, trying to synch their beats together.

Sans watched with bated breath as they both beat together for a count, lust blossoming in his chest at the sight. Frisk’s soul was having trouble staying at the same lethargic pace as Sans’ soul- they would beat together for a moment and then Frisk’s would speed up before slowing back down to re-match the other.

Frisk watched Sans’ magic swirl, dip, and dance inside his body as he watched their souls work together. It was hard not being able to see the expressions on his skull, but after years of learning how to read his magic and how it reacted to his emotions, Frisk knew exactly what he was feeling. To them, it was plain as day as if his magic was simply spelling out his emotions to them. Lust, love, excitement, adoration… It was all there.

“I want this, Sans. I know I’m young, that our relationship is the first of its kind in centuries, that this is all a complete unknown to us… But I’ve never wanted anything more in my life.” Frisk whispered, looking up to where they knew Sans’ face was. Small tears gathered up in the corners of their sockets as their pupil-less brown eyes stared up at Sans.

“stars, frisk. you… i…” Sans couldn’t get the words out in a proper order, his mind too jumbled to form a proper sentence. “i… i love you.”

With those three words hanging in the air between them, it felt like something finally clicked. Frisk’s soul slowed down and began beating in time with Sans’, pulsing with light as they finally synched up and settled together.

Frisk reached up and grabbed Sans’ skull, pulling him down into a hungry kiss. Their teeth mashed against his in their frenzy, desperately needing something to ground them and convey what they were feeling to the skeleton.

“I love you, I love you, I love you,” Frisk chanted between kisses, tears rolling down the side of their face. “You’re so amazing and I can’t believe that you’re mine, you’re mine and we’re mates. You’re mine!”

Practically growling that last part, Frisk pulled Sans even closer as they wrapped their legs around his hips and their hands pawed against the front of his ribs. Sans relished in the contact, low groans sounding in the back of his throat as her kissed Frisk back with intensity. His hands were gripping their waist, fingers digging into the soft flesh as he grinded his hips down.

“frisk… baby, hold on,” Sans panted, pulling back from the body beneath him. “do you want to actually complete this right now? the whole thing?”

Frisk nodded without missing a beat and moved to sit up. Sans backed up and sat down on his legs in front of them as they got into a comfortable position.

“… ready?”

“Hell yes.”

Chuckling, Sans reached forward and with a tugging motion, pulled Frisk’s soul out of their chest. The familiar candy red soul pulsed with energy, still beating at a lethargic pace that echoed Sans’. It covered the room in bright red shadows, illuminating the two faces that were staring at it. Frisk made eye contact with Sans and his magic pulsed with approval. They copied Sans’ actions, reaching forward and doing a tugging motion to pull out his soul. The upside down soul was even brighter than Frisk’s own, washing out the red with white to create soft pink hues that dusted the walls.

The pair of souls bobbed gently in the air, slightly gravitating around each other as they slowly pulled closer and closer. Frisk and Sans watch with a heavy gaze, letting the souls do what they were meant to do in this situation. Closer, closer, yet closer, the two of them got until they made a small brush of contact. Like a switch being flipped, the two souls thrust together, red and white mixing into a beautiful pink where they touched.

Pushing closer, the two souls seemed to almost meld into one before separating with a wet sound. Hovering together, the changes were obvious as Frisk and Sans looked over them. Sans’ soul had a red ring on the outer edge and Frisk’s had a white ring around their red. The feeling of love was pouring from both souls as they bobbed in time together, touching once more before gently drifting away and back into their respective hosts.

“Oh…” Frisk whispered, covering their chest with the hands as warmth enveloped their body.

“you can say that again, kiddo…” Sans’ voice was quiet as he let the emotions rush over his own frame. He could easily feel the second pulsing of a soul inside his body, evidence of Frisk’s soul being alive and healthy.

“I love you.”

“i love you, too.”

Frisk reached for Sans, fully intending to pull themselves into his lap to curl up and lay their head on his chest. Sans grabbed their outstretched arms and pulled them into his lap, wrapping his arms around their waist and nuzzled his teeth against their forehead. Frisk hummed with pleasure, pushing themselves closer, wrapping their hands around his ribs and placing a chaste kiss on Sans’ exposed collarbone.

“Sans, can we-“

Frisk was cut off by a loud, mechanical clank, that was followed by the sound of mesh clinking together. Silence followed the random noise, Sans and Frisk both staring down at Frisk’s lap.

“did it just… come off?” Sans asked, hands twitching with the need to investigate.

“Uh, I think so? Let me just…” Frisk scooted out of Sans’ lap and towards the edge of the bed. As they moved, the mesh jingled together, making it obvious that the chastity belt had indeed unlocked itself. Sans glanced at the clock on his bedside table and it read exactly midnight.

Frisk pushed themselves off of the bed and their shorts instantly fell around their ankles, leaving them bare from the waist down. They squeaked and quickly dropped to the floor, wrapping their arms around their knees in embarrassment. Sans began laughing at the situation that had just unfolded in front of him, tears gathering in the corners of his sockets from how hard he was laughing.

“oh my god, you just got pants’d by your own chastity belt,” Sans wheezed, slapping his bed as he laughed. “i can’t believe that jus’ happened!”

“Sans! It isn’t funny!” Frisk scolded as they removed the remains of the mesh contraption from the insides of their shorts.

“sure it is, babe! you shoulda seen your face!”

Frisk huffed in annoyance, peering over the edge of the bed at Sans. His magic was slightly pooling in his pelvis, evidence that while he was finding the situation hilarious, he had been slightly turned on by seeing Frisk’s bare ass. A devious plan began forming inside Frisk’s mind and they let a smirk slide onto their face.

“oh stars, i haven’t laughed that hard in a while,” Sans leaned back on the bed as he tried to catch his breath. “that was hilarious.”

“Oh, yeah?”

“hell yeah it was!”

Frisk pulled themselves back onto the bed and began crawling towards Sans, who still had his skull tilted back as he caught his breath. They slowly climbed into his lap, straddling his hips, before sitting back and brushing against the slight bulge that was beginning to form there.

Sans’ skull snapped up at the sensation, eye lights growing as he realized what was happening. With a coy smile, Frisk grinded into Sans again, letting their bare folds brush against the fabric of his shorts.

“You still think it’s funny, Sansy?” Frisk purred.

Sans shook his head no, jaw dropped as he watched the scene in front of him unfold. He lifted his hands and grabbed Frisk’s hips, pushing them down to grind against his erection again and let out a groan at the feeling.

“stars, you’re so hot and wet down there…” Sans whispered as he rubbed circles into Frisk’s skin with his thumb.

Frisk didn’t respond and instead reached down to pull their sweater over their head, leaving them completely naked in Sans’ lap. They tossed the shirt off to the side and it landed with a thump somewhere in the room. Sans was watching every move Frisk made with lust filled eyes, his magic thrumming with lust.

His mate, his lover, his life was baring themselves to him completely and he was just sitting there watching instead of doing anything. With a growl, Sans grabbed Frisk’s ass and pulled them closer to him. They let out a squeak at the sudden movement but was quieted by Sans as he kissed them with pure want and lust. He opened his jaw to flick his tongue across their lips, asking for entrance and when Frisk’s mouth opened he delved in and began to explore. His tongue left nothing untouched as he ravished their mouth, tugging their tongue out so he could twist his own around it in a battle of play-dominance.

Frisk mewled as Sans dominated them, letting their arms wrap around his neck so they could lean into the kiss even more. They were completely at his mercy as he claimed them, not even bothering to try and battle him as he wrestled with their tongue. While Frisk enjoyed playing the dominate and teasing Sans outside of the bedroom and in less heated situations, when it came to the real thing they were completely submissive to the monster.

“i love you, frisk. so much…” Sans murmured as he let them catch their breath after the intense make out session. He peppered small kisses across their face, his teeth pressing against any skin that was close enough to reach. He watched their chest heave as they breathed, breasts rising and falling with the movement of their lungs. Sans pushed them back a little so he could pull his own shirt off, tossing it away, before pulling Frisk flush against his chest.

He could feel their ribs pressing into his, their nipples hardening at the new sensation of skin to bones. Frisk moaned at the contact and Sans’ breath hitched at the sound. He wanted to hear more of that, to make a symphony of noises inside his bedroom as he claimed them tonight. He cupped a hand around Frisk’s ass, lifting them slightly as he used his other hands to try and push his shorts down. Sans didn’t make it far, growling with protest as his shorts refused to slide down his bones.

“Here, hold on,” Frisk chuckled. They placed their hands on Sans’ shoulders and braced themselves there as they lifted their hips to make it easier for Sans to remove his shorts. As soon as they were down far enough, Sans kicked them off and let out a sigh of pleasure to have the clothing gone.

A glowing blue cock rested against his hips, and Frisk stared at it in shock. They didn’t think something so thick could actually fit inside them, let alone belong to a skeleton! They settled back down on Sans’ femurs and reached out to touch it. Sans let out a groan when their fingertips brushed against the head, dick twitching with arousal.

“keep touching it, baby… please…” Sans begged, his eye sockets hooded as he watched them.

Frisk nodded and wrapped one of their hands around the base of his cock, lightly stroking upwards. It was smooth to the touch, with small bumps here and there that Frisk assumed it was how Sans imagined it. The more they pumped it, the brighter it seemed to shine and Frisk wondered how bright they could get it before Sans came. Determination filled their soul and they pumped Sans’ dick with more enthusiasm.

“o-oh, fuck! yes, yes, yes, baby, please keep going! i-i’m so close,” Sans moaned, bucking his hips in time with Frisk’s movements. “stars, i l-love you! i’m gonna cum, oh f-fuck!”

With one final thrust, Sans came, his cum spilling over Frisk’s hand that was still wrapped around his cock. The blue tint of his cum stood out in the darkness and against their dark skin as it dribbled down their hand. Frisk made eye contact with Sans, who was breathing heavily and already watching them, as they unwrapped their fingers from around Sans’ and lifted it towards their mouth. Sans’ eye sockets widened when he realized what they were about to do, jaw dropping in shock.

Frisk winked before pushing their tongue out to lick off Sans’ cum from their hand. They kept eye contact the entire time as they lapped up every last drop that was on their hand. Sans could feel his magic buzzing with renewed lust at the sight and it took every ounce of his willpower not to pounce on them and fuck them into the mattress.

“Still taste like blue raspberries.” Frisk mused, smacking their lips and smiling.

“you’re so beautiful, frisk,” Sans stated, pushing on their shoulders slightly.

They fell backwards with a giggle, bouncing slightly as they landed on the bed. They opened their arms and lifted their hips, inviting Sans to nestle between their legs. He shuffled between their legs, lifting them to rest against the tops of his hips.

“do you want me to…?” Sans asked, looking down at Frisk who stared back up at him with pure love written across their face.

They shook their head no, mouthing an ‘I love you’ as they lifted their hips up farther. They were ready for this- ready to be Sans’, to be claimed. They didn’t need him to return the favor because they had plenty of time tonight to catch up on lost time. Frisk just needed him and couldn’t wait any longer.

Sans grabbed his cock and pushed it against Frisk’s entrance with a mix of anxiety and excitement. He rubbed the head of his shaft up and down against their slit, teasing them as they wiggled in his grasp. Sans knew this was their first time and while he didn’t want to hurt them more than he had to, he wasn’t sure if he could hold himself back once he gets a taste.

“Please…” Frisk whimpered, begging Sans to finally take them as they pushed their hips towards him.

That one word snapped all of the hesitations Sans was having and in one swift movement, he buried the head of his cock inside Frisk. They tensed at the sudden intrusion but relaxed and nodded, motioning for Sans to keep going. He pressed in farther and he could feel the velvety walls sliding over his dick as he went farther. Frisk was panting beneath him, eyes clouded over in pain as Sans stretched them in a way that was foreign to them. It wasn’t entirely unpleasant, but the pain was slowly fading.

After a few long, agonizing, minutes Sans hilted within Frisk and they both let out a sigh of pleasure. The feeling of being so full was so satisfying to Frisk and they raised their arms, silently asking Sans to bend downwards so they could kiss him. He obliged, slowly leaning forward and wrapping his own arms around Frisk’s waist. This made his cock slip even deeper into Frisk and they both let out a groan at the sensation.

Sans tugged them to him and kissed them fiercely, trying to hold himself back from thrusting into them before they gave him permission. Their walls were so tight around him and he wanted to feel them sliding against his dick, moaning underneath him as he wrecked them.

Frisk returned the kiss with fervor, opening their mouth to lick at Sans’ teeth. He returned the gesture, opening his mouth to allow Frisk entrance. Frisk wiggled as the kiss deepened, eliciting a groan from Sans. They bucked against him, silently telling him to move, too busy kissing him to actually speak.

Taking the hint, Sans slowly pulled his hips back before sliding back into Frisk. The feeling of their walls practically sucking his dick back in was too much and he let out a growl at the sensation. He repeated the motion a few more times, slowly dragging out and slowly thrusting back in as Frisk keened beneath him, grabbing at his ribs. They ran their fingers across his sternum and across his ribs, nicking him slightly with their fingernails. Sans shivered at the sensation and his control slowly started slipping as Frisk continued touching his bones.

After a particularly rough scratch to the underside of his lower ribs, what was remaining of Sans’ control snapped.

“you’ve fucking a-asked for it, frisk…” Sans growled, pressing all the way into them. Frisk let out a loud moan and Sans smirked. “hold on tight, sweetheart.”

Sans pushed as far as he could into Frisk, poking at the beginning of their cervix with the head of his cock. Frisk panted underneath him, small moans of pleasure huffing through their lips as they lifted their hips for him to push deeper.

“Yes, oh my god, Sans,” They breathed, arching their back.

Sans ducked his head to take one of Frisk’s breasts into his mouth and bit down lightly on the nub. When Frisk opened their mouth in a gasp, he pulled and slammed back into them, making them choke on their breath. Small whimpers escaped instead as they clung to his ribs, tugging on them to tell him to continue.

He set a hard and rough pace, pulling almost all the way out before slamming back into Frisk, reveling in the delicious sounds that spilled from their lips. They were repeating his name as if it were a prayer that could bring them ultimate completion, and in a way it would. The way that Frisk was writhing under him awakened something deep inside his soul that he thought he would never touch again; pure motivation.

Sans wanted to make them forget all that they knew until all they could think of was him. He wanted to break them, destroy their mind with pure pleasure as he took them as his in any way that he wanted. He wanted this so much, wanted them so much.

“so good… you feel so damn good wrapped around my cock like this,” Sans praised, slowing down to grind against Frisk. “you’re so damn beautiful, just look at you. you’re a damn mess, but you want more, don’t you, baby?”

“Oh, stars, yes,” Frisk whispered, eyes closed as they grinded in time with Sans. “I’m so close, please let me…!”

“say it. gotta tell me what you want, if you want want it.”

He pulled out slowly, teasing Frisk as they cried out in annoyance. The feeling of being empty when he pulled away was almost too much for them to handle. In such a short time of finally being able to join together, Frisk was already addicted to the feeling. They craved, no they _needed_ , completion.

“P-please… let me… c-cum…” Frisk mumbled, turning their head away so Sans couldn’t see the embarrassment on their face.

“mmm,” Sans pulled out even farther, the head of his cock barely still inside them. “couldn’t hear you. what was that?”

Throwing their dignity out the door due to pure desperation, Frisk screwed their eyes shut. “I said, please let me cum!”

“good girl. that’s what i like to hear.”

Instead of having Sans slam into them again, like Frisk was expecting, he slowly sunk back into them. Sans let out a low groan, the sound sending a shiver down their body. He made such lewd sounds and was so lost in the feeling, it made Frisk even more excited.

Sans leaned down to press his forehead against Frisk’s sockets shut tightly as he thrusted slowly, dragging out the inevitable. It was coming to a close for both of them- Frisk could feel the coil in their stomach tightening as Sans slowly pushed them to completion and Sans could feel his magic drumming with an erratic tempo inside his body.

Time seemed to slow around the two of them as they were wrapped up in each other’s arms, their legs wrapped around his waist and his arms under the back to lift their hips. Slow thrusts drug soft moans from both of their mouths as they basked in the feeling of ecstasy of coming to completion together for the first time. Sans could feel Frisk’s walls tightening around his cock and he tried to stop himself from finishing first from the overwhelming sensation.

“b-baby… i don’t think…”

“I’m so c-close… just go,” Frisk panted, pulling his lips to theirs in a kiss.

With an obliging grunt, Sans picked up the pace. He thrust into them with unsteady strokes, trying to stave off his own orgasm so Frisk could go first. They were clenching his cock so tightly it was almost painful trying to keep the pace.

“S-sans, oh my gods…”

“cum with me, frisk. please, please, please,” Sans mumbled against their lips.

As if he had spoken the magic words, Frisk’s walls fluttered against his dick as they tipped over their peak, dragging his own orgasm out of him. He came inside them as Frisk held him close, whispering his name in reverence. Sans’ bones rattled as he continued to spurt rope after rope of cum inside their body, shaking with love and exhaustion. Frisk clutched at his shoulders, small moans escaping in the breaks of repeating his name.

After a few minutes of riding out their climaxes together Sans’ magic dissipated, leaving Frisk empty. Glowing blue semen slowly flowed out between their folds, dripping down onto the crumped sheets.

“that was…”

“Exhilarating. Amazing. Wonderful. Great.” Frisk supplied, grinning wildly as they stared up at him.

Sans chucked as he fell to the side and pulled Frisk towards him, tucking their body against his. Their head fit comfortable under his chin, cheek pressed against his sternum. Frisk’s fingers traced designs on his ribs as his fingers combed through their hair. The afterglow of such a wonderful experience that had been a long time coming left them in stunned silence. Minutes ticked by in silence as the two of them continued to pet each other and listening to the synchronized beating of their souls.

“So… When do you think you’ll be good to go again?” Frisk lifted their head to shoot Sans a mischievous grin.

Sans stared down at them in shocked silence before breaking out in a wide grin. He flipped them over with a laugh as Frisk shrieked with surprise, peppering their face with kisses as his hands grazed down their body. Sans grabbed their ass and lifted their hips so he could nestle between them again.

“right now. and in ten minutes. when we shower. in the morning when we go make breakfast,” Sans smirked, squeezing their flesh. “i’ll always be good to go again.”


End file.
